1. Field of the Invention
This invention relates to an access control apparatus for a disk storage device employing, in particular, a constant density recording CDR mode, which apparatus has an address translating function for translating logical block addresses supplied from a host computer to physical block addresses. The invention also relates to an address translation method employed in the apparatus.
2. Description of the Related Art
In the case of a conventional disk storage device such as a hard disk drive (HDD), the both opposite surfaces of a single disk or of each of disks are used as data surfaces, into and from which data items are recorded and reproduced. This device has a plurality of heads corresponding to data surfaces (e.g., two heads for a single disk), and read/write of data is performed by moving the heads in search of a target track on a target data surface and positioning one of the heads to the target track.
The data surface has many concentric tracks formed from its radially outermost portion to its radially innermost portion. The tracks which are formed on corresponding portions of the data surfaces are included in the same cylinder, and have the same address code consisting of a recognition track number (cylinder number). Further, each track has a plurality of sectors. In the disk storage device, data access is performed in units of a sector.
A host computer supplies the disk storage device with a logical block address which is irrelevant to a data-stored portion of a disk, when it performs data access (read access or write access). Then, the disk storage device translates the logical block address to a physical block address which is necessary to perform data access on the data surface of a disk in units of a sector. The physical block address is address data consisting of a head number, a track number, and a sector number.
The above address translation is performed by a controller (HDC) employed in the disk storage device. To designate physical block addresses, the HDC sequentially designates track numbers of a data surface corresponding to, for example, a head with a minimum head number (usually 0), from a radially-outermost-track number to a radially-innermost-track number. When the HDC reaches the radially-innermost-track number, it increases the head number from 0 to 1. On the contrary, the HDC may designate track numbers from the radially-innermost-track number to the radially-outermost-track number.
Recently, a disk storage device has been developed, which employs a constant density recording (CDR) mode. As is shown in FIG. 2, in the case of the CDR mode, the data surface of a disk 20 is divided into many concentric blocks called "zones", and each zone is divided into several tens--several hundreds of tracks. FIG. 2 shows a data surface divided into only three blocks 0, 1, and 2, for easy understanding. In this case, each of the tracks included in zone 0 has sectors 0-9.
Each track included in zone 1 is divided into sectors 0-7 in this case. Similarly, each track included in zone 2 is divided into sectors 0-5. In other words, more data items can be written at a higher transmission rate into the radially outermost zone 0 than into the radially inner zones 1 and 2.
Therefore, in the disk storage device employing the CDR mode, each time the zone to be accessed is changed from one to another at the time of reading/writing data, it is necessary to change the frequency of a write reference clock used in a read/write circuit, the gains of an analog filter and a PLL (phase-locked loop), etc., in accordance with data transmission rate set in each zone.
As is shown in FIG. 3A, each sector has an ID area 32 storing ID data for identifying the sector, and a user area 33 for reading/writing data when the host computer has accessed it. Further, as is shown in FIG. 2, in the case of the sector-servo type HDD, servo data items are prestored in the data surface of the disk 20 at regular intervals.
As is shown in FIG. 3A, servo data is stored in an area, which consists of an address data area 30 storing an address code corresponding to its track number (cylinder number), and a burst data area 31 storing a burst pattern to be used to position the head to the center of the track. In the case of a usual HDD of a type other than the CDR, servo data is stored in the tip portion of each sector.
In an HDD of the CDR mode, however, since the number of sectors in a zone differs from that in another zone, servo data is not necessarily stored in a tip portion of each sector. FIG. 3A shows an example of a format for e.g. sector 0 of zone 0. In this format, servo data is stored in a tip portion of sector 0. On the other hand, FIG. 3B shows an example of a format for sector 3 of zone 0. In this format, the areas 30 and 31 storing servo data are located such that they divide the user data area 33 into two portions. The same can be said of zones 1 and 2.
Actually, the host computer often sequentially accesses data items stored in a plurality of blocks (which are defined in units of a sector) by outputting a series of logical block addresses. If the above-described method of sequentially designating physical block addresses is employed in the CDR mode at the time of translating serial logical block addresses to physical block addresses, zone changing occurs many times. If the disk has a large number of zones, zone changing occurs too many times.
Specifically, where the number of zones is 10 and that of heads is 8, the number of changes of zones per one pass for designating a physical block address is 80 (=10.times.8). Since, as described above, the frequency of the write reference clock in the read/write circuit, etc., must be changed at the time of changing zones, a predetermined time period is required to perform zone changing. Increasing the time period required for zone changing in accordance with an increase in the number of occasions of zone changing will result in a reduction in the access rate of the disk storage device.